1. Field of the invention
The present invention relates, in general, to the process for preparing an industrial polyester multifilament yarn, and in particular, to a process for preparing an industrial polyester multifilament yarn with a high modulus and a low shrinkage, in which a treated cord produced from the polyester multifilament yarn has an excellent dimensional stability and tenacity, and can be applied to fiber reinforcements for use in rubber products such as a tire and an industrial belt or to other industrial applications.
2. Description of the Prior Art
High strength polyester fibers have been used in various applications such as a tire cord for reinforcing rubbers, a seat belt, a conveyer belt, a V-belt and a hose. Particularly, a treated cord converted through a latex and heat treatment for the use of a fiber reinforcement of tires requires an excellent dimensional stability and tenacity.
U.S. Pat. No. 4,101,525 (Davis et al.) and U.S. Pat. No. 4,491,657 (Saito et al.) disclose industrial polyester multifilament yarns having a high initial modulus and a low shrinkage. Since then, efforts have been made to produce high strength yarns at a faster spinning speed.
Generally, it is a well-known art in the industrial polyester high modulus low shrinkage yarn industry that the higher the spinning speed is, in the range of 2,000xcx9c3,200 m/min, while high intrinsic viscosity (I.V.)is used, within the preferred range of intrinsic viscosity(I.V.) 0.9xcx9c1.2, if the polymer and spinning temperature are the same, then the more the dimensional stability of treated cords and the strength retention of yarn to treated cord will be improved.
Theoretically, the dimensional stability of final treated cord and the strength retention to cord of the yarns can be increased by increasing a spinning tension of an industrial polyester yarn and increasing an orientation of undrawn yarns and a formation of a tie chain connecting crystals to each other. To produce higher strength treated cord, uniformity in the filament fineness and in the orientation level of undrawn yarn should be improved so that highly oriented undrawn yarns can be drawn at a high draw ratio.
In this perspective, improved polyester multifilament yarns with a high modulus and a low shrinkage can be produced by providing more uniform undrawn yarns under quick quenching (generally, the quicker the quenching is, the less uniform yarns are obtained)
According to U.S. Pat. No. 3,858,386 (Richard H. Stofan) and U.S. Pat. No. 3,969,462 (Richard H. Stofan), it is described that uniform undrawn yarns can be advantageously produced by a radial in to out quenching method, in view of evennees of yarn and a uniformity of tenacity and elongation. However, this radial in to out quenching method is only used to produce high strength polyester yarns at 1000 m/min or less.
According to U.S. Pat. No. 4,285,646 (Roland Waite), cooling gas is supplied through a spinning pack in a radial in to out flow quenching method, but this method is very difficult to carry out.
According to U.S. Pat. No. 4,414,169 (Edward B. McClary), a radial in to out quenching device is used, but the quenching device is unsuitable to be used to produce yarns for a polyester low shrinkage and high modulus tire cord yarn above 1000 deniers based on final drawn yarns, because the quenching device has a diameter of 1.5 inches and a length of 36 inches and a feed rate of cooling air is insufficient.
Furthermore, U.S. Pat. No. 5,866,055 (Raimund Schwarz et al.) discloses a process for producing an improved polyester multifilament yarn with a high modulus and a low shrinkage by use of a radial in to out quenching method.
According to this method, an uniform quick quenching is theoretically possible, however, high viscosity spin finish should be used in order that the spin finish oil would not be blown off because the spin finish oil is supplied to each filament directly below a radial in-to-out quenching device by a disk-type device for supplying the spin finish oil, and much damage ca be done to the spin filaments because the quenching of spun filaments becomes insufficient to contact yarns with the device for supplying spin finish oil near to the nozzle, in comparison with a conventional method in which yarns are contacted with the spin finish oil device near to take up roller.
Therefore, the process for producing an improved polyester multifilament yarn with a high modulus and a low shrinkage, which has a high spinning stress, by use of a high speed spinning method according to U.S. Pat. No. 5,866,055 has disadvantages in that it is difficult to produce heavy denier yarns above 1000 deniers at a high speed above 2000 m/min because the uniform of spin finish oil pick up and the uniformity of the stress applied to spun filaments are poor.
Therefore, it is an object of the present invention to provide a process for manufacturing an improved polyester multifilament yarn with a high modulus and a low shrinkage used in a production of a tire core, in which the heavy denier polyester multifilament yarn of 1000 deniers or more can be prepared by improving a uniform pick up of spin finishes and a uniformity of the tension among spinning filaments and using spin finishes with a relatively low viscosity, preferably aqueous emulsion spin finishes, with the use of a radial in-to-out quenching method at a spinning speed above 2,000 m/min. The radial in-to-out flow quenching method improves a quenching uniformity among filaments by blowing cooling air from inside to outside to a bundle of filaments below a spinning nozzle, by using a cylindrical device with a filter for blowing out cooling air.
Furthermore, the industrial heavy denier polyester multifilament yarn of 400 deniers or more produced at a spinning speed below 1,000 m/min according to the present invention is improved in the cross section CV% between filaments above 20% without effecting a big variation of the other physical properties.